Cardiac arrhythmia are common and potentially dangerous medical aliments associated with abnormal cardiac chamber wall tissue. Characteristic of cardiac arrhythmia, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normal cardiac tissue. The abnormal cardiac tissue regions conduct electrical activity to adjacent tissue with aberrations that disrupt the cardiac cycle, creating an asynchronous cardiac rhythm. Various serious conditions, such as stroke, heart failure, and other thromboembolic events, can occur as a result of cardiac arrhythmia.
One particular type of cardiac arrhythmia is atrial fibrillation (AF). Atrial fibrillation is recognized as the most common clinically significant cardiac arrhythmia and increases significantly the morbidity and mortality of patients. Current data estimates that 2.3 million Americans experience AF. Since the prevalence of AF increases with age, and due to the aging population, the number of AF patients is estimated to increase 2.5 times during the next 50 years.
Atrial fibrillation usually results in a rapid ventricular rate and an irregular ventricular rhythm that produce undesirable negative hemodynamic effects. Long-term uncontrolled rapid ventricular rate could, for example, lead to tachycardia-induced cardiomyopathy. Irregular ventricular rhythm may independently produce detrimental consequences and may cause symptoms in some patients, even when the ventricular rate is controlled. It is therefore desirable to achieve ventricular rate control and ventricular rhythm regularization during AF.
A variety of medical procedures have been developed to help treat cardiac arrhythmia. Drug therapy is the most common approach to achieve slow ventricular rate in AF patients. Drug therapy may, however, may be ineffective or not well tolerated. Partial ablative procedures, such as AV node modification, have been shown to be effective in reducing ventricular rate in some drug-refractory AF patients. However, due to the risk of AV block associated with AV node modification, this therapy is recommended only when AV nodal ablation with pacemaker implantation is intended. Although AV nodal ablation with right ventricular pacing has been shown to be beneficial in improving symptoms, quality of life, and exercise duration in drug-refractory patients with AF, it creates permanent AV block and results in lifelong pacemaker dependency.